Amti range ambiguity resolver

ABSTRACT

In a pulsed energy system, employing higher PRF&#39;&#39;s for increased data rates, means for reducing the range ambiguity in moving target data associated with range time intervals in excess of the pulse repetition interval. A plurality of radar data matrix storage means is employed, each representing a like plurality of successive range trace intervals, a preselected range time increment or difference existing between successive ones of the radar data matrices. A doppler buildup at a like range bin in each of the matrices describes a moving target at less than an ambiguous range, however, a doppler buildup at a mutually exclusive range bin in each of the three matrices indicates a target in any ambiguously indicated, but determinable, range. Logic means responsive to the condition of the difference between the ambiguous range indications, relative to the preselected range difference between the matrix storage means, determines that range compensation term to be added to an indicated range for purposes of an unambiguous MTI range trace display.

Uite States atet [111 3,765,017

Dentino Oct. 9, 1973 AMT! RANGE AMBIGUITY RESOLVER increased data rates,means for reducing the range [75] Inventor: Mauro Joseph Dentin,Placemia ambiguity in moving target data associated with range Califtime intervals in excess of the pulse repetition interval. A pluralityof radar data matrix storage means is em- [73] Asslgneei Nm'th AmencanRockwell Corpo' ployed, each representing a like plurality of successiveration El Segundo! Califrange trace intervals, a preselected range timeincrew 1 ment or difference existing between successive ones of [22]Filed. June 1968 the radar data matrices. A doppler buildup at a like PP738,722 range bin in each of the matrices describes a moving target atless than an ambiguous range, however, a 52 us. Cl. 343/7.7,'343/9buildup at a f l W range in 51 11m. Cl. @015 9/42, GOls 9/44 each, 0fthe P mamces mdlcafes a large m 58 Field of Search 343/71 9 17.1ambguously mdcated' but range' Logc means responsive to the condition ofthe difference [56] References Cited between the ambiguous rangeindications, relative to the preselected range difference between thematrix UNITED PATENTS storage means, determines that range compensationl Elbinger term to be added to an indicated range for purposes of I anunambiguous MT] range trace display. Primary ExaminerBenjamin A.Borchelt Assistant ExaminerG. E. Montone Attorney-William R. Lane, L.Lee Humphries and R lf M Pi 6 Claims, 12 Drawing Figures [57] ABSTRACTIn a pulsed energy system, employing higher PRFs for SYSTEM TRIGGERINPUT mm -REFERENCED fig} VIDB) INPUT FROM I5 RADAR RECEIVE IO U 'l I 1I8 F l I I counr I now I 1 MASTER I I CL\OCK it I I PRF I I 1 I I4 I I IPRF *2 I I I I2 I I 20 '1 l I PRFJE' 3 a od PLER DOPPLER I $TORAGE*arouse -4e t E N t MEANS #2 I 1 runssnoto DOPPLER /-22 FILTER l I I ISECONDARY I STORAGE 1 I CHANNEL CHANNEL CHANNEL 1/ RANGE INTERVAL o it*2 I #3 I :RESOLVER f LOGIC ELEMENT TARGETING COMPUTER PATENIED 919153.765.017

sum 30F 5 lNVENT f-R. MAURO J. DENTINO ATTOR NEY PATENTED BET 91975SHEET 5 BF 5 TIMING DIAGRAM SEQUENCE mifi igwr n90 RANGE BINS STORED IN.l97sec.

wRrrE-lN I250 RANGE BINS CHANNEL #2 STORED IN .207

WRITE-IN l3|0 RANGE ems CHANNEL 3 STORED IN .2l7sec READ-OUT AND RESOLVEALL AMBIGUOUS RANGE INTERVALS l o .l97 .404 .62l .8l8 L035 TIME(SECONDS)--I ElGs MAURO J. DENTINO ATTORNEY ll AMTI RANGE AMBHGUITYRESOLVER CROSS REFERENCES TO RELATED APPLICATIONS 1. U. S. PatentApplication Ser. No. 391,073 filed Aug. 18, 1964, by Forest J. Dynan,etal, for AMTI Radar System.

2. U. S. Patent Application Ser. No. 639,238 filed May 17, 1967, byJames A. Moulton for Range- Gated Moving Target Signal Processor.

BACKGROUND OF THE INVENTION In the airborne application ofdirectionally-ranging pulsed energy systems, such as radar systems, itis often desired to detect and locate small moving targets against alarge clutter background. Where such a moving target is moving radiallyof the radar system relative to the clutter background, such detectionof the target is sought by means of the difference in the respectivedoppler shifts of the echo return signals from such target and theclutter background, as is well understood in the art. Descriptions ofsuch doppler processing techniques for coherent and non-coherent radarsmay be found in U. S. Pat. No. 3,341,847 issued to W. R. Fried, et al,for Platform Motion Compensation of a Coherent MTI System and in U. S.Patent Application Ser. No. 391,073 filed Aug. 18, 1964, by F. J. Dynan,et a] (now US Pat. No. 3,408,647), and in U. S. Patent Application Ser.No. 639,238 filed May I7, 1967, by James A. Moulton, both of whichapplications are assigned to North American Aviation, Inc., now known asNorth American Rockwell Corporation, assignee of the subject invention.

As disclosed in the above-noted U. S. Pat. No. 3,408,647, such dopplerprocessing involves the storage of a radar data matrix of theclutter-referenced range trace signal or each return of a preselectednumber of successive pulse repetition intervals. Such clutter-referenceddata matrix is alternatively referred to herein as a doppler map for thereason that by crossscanning or doppler integration of such matrix bysequentially scanning a like range bin or portion of successive ones ofthe stored range trace signals, the doppler content at such range binmay be recovered, selective bandpass (doppler) filtering being employedto reject the clutter content thereof.

An inherent limitation in such doppler processing is the existance ofblind speeds or target velocities at which targets may not be detected,due to such speeds being represented by doppler frequencies lying withinthe bandwidths of the radar pulse repetition frequencies which arerejected by the upper bandpass limit of the doppler filter. Anotherlimitation inherent in a conventional AMTI radar system is the limiteddata rate imposed by the required dwell time to obtain enough samples orrange trace signals from which to satisfactorily construct the dopplermap and recover the moving target signal, free of clutter.

Increasing the pulse repetition interval of the pulsed energy systemwould increase the rate at which data may be obtained from a smalltarget as to allow improved detection thereof: improvement in targetsignalto-noise ratios, improvement in doppler processing rates, andreduction of blind velocity regions. Where the pulse repetitionfrequency is varied, the blind speed region may be further reduced.However, where the pulse repetition intervals (PRIs) of such increasedpulse repetition frequencies (PRFs) are much less than the nominal ormaximum intended range of the radar, the target returns will beambiguous in range. In other words, the received echo of a transmittedpulse, representing the target return, will occur during other than thepulse repetition interval immediately subsequent to such pulse, wherebythe determination of the apparent range time occurrence of the targetreturn within that pulse repetition interval in which it is receivedwill not be indicative of the true range of the target.

Prior art means for resolving the range time ambiguities in pulsedenergy systems employing increased PRFs have included the use of afrequency-hopping transmitter and an associated plurality of switchednarrow bandpass the receivers, a given one of the receivers beingswitched-on for a preselected interval in synchronism with thecorresponding discrete transmitter frequency, as taught for example inU. S. Pat. No. 2,817,832 issued to R. H. Mathes for Multiple Sweep.However, such arrangement employs several separately pulsed transmittersof different frequencies and parallel receiver channels, and does notcomprehend the use of a single-frequency transmitter and single channelreceiver. Nor does such technique relate to either doppler-processing ofsuch signals by means of a single doppler bandpass filter of thevariation of PRF to reduce blind speed regions.

In other words, the prior art, in providing either doppler processing ormultiple sweep (higher PRF) systems for enhancing detection of smallmoving targets, yet does not provide means for advantageously combiningthese functions.

SUMMARY OF THE INVENTION By means of the concept of the subjectinvention, the several features of doppler processing and multiple PRFsat increased rates are combined to effect improved detection of smallmoving targets while resolving range-ambiguities and reducing blindspeed regions.

In a preferred embodiment of the inventive concept, there is provided apulsed energy system sequentially employing at least two higher PRFs forincreased data rates. There is further provided means, including dopplerprocessing, for reducing the range ambiguity in moving-target dataassociated with range time intervals in excess of the pulse repetitionintervals. A plurality of radar data matrix storage means is employed,each representing a like plurality of successive range trace intervals,a preselected range time increment or difference existing betweensuccessive ones of the radar data matrices. A doppler buildup at a likerange bin in each of the matrices describe a moving target at less thanan ambiguous range; however, a doppler buildup at a mutually exclusiverange bin in each of the three matrices indicates a target in anyambiguously indicated, but determinable, range. Logic means responsiveto the condition of the difference between the ambiguous rangeindications, relative to the preselected range difference between thematrix storage means, determines that range compensation term to beadded to an indicated range for purposes of an unambiguous range tracedisplay.

Accordingly, it is an object of the subject invention to provide meansfor enhanced detection of small moving targets.

it is another object of the invention to provide means for reducing therange ambiguities associated with utilization of higher lPlRFs in apulsed energy system;

It is a further object of the invention to reduce the blind speedregions associated with doppler-processing in a moving target indicatortype pulsed energy system.

Still another object of the invention is to combine the use of at leasttwo higher PRFS and doppler processing techniques to enhance detectionof small moving targets and reduce both blind speed regions and rangeambiguities.

These and other objects of the invention will become apparent from thefollowing description, taken together with the accompanying drawings, inwhich:

BRIEF DESQREIPTION OF THE DRAWlNGS PKG. 11 is a block diagram of asystem embodying the inventive concept;

H6. 2 is a family of representative time histories of the response ofthe multiple PREP transmitter arrangement of HG. ll;

FIG. 3 is a family'of representative time histories of the response ofthe system of HG. l to a target at a preselected non-ambiguous range foreach of the several pulse repetition frequencies employed;

FIGS. 40, lb and 4c are representative doppler maps constructed for thesystem responses of FIG. 3 for each of the pulse repetition frequenciesemployed;

F IG. 5 is a family of representative time histories of the response ofthe system of FIG. l to a target at a preselected range within a firstambiguous interval, for each of the several pulse repetition frequenciesemployed; I

FIGS. 60, 6b and 6c are representative doppler maps constructed for thesystem responses of FlG. 5 for each of the pulse repetition frequenciesemployed;

FIG. 7 is a family of representative time histories of the response ofthe system of HG. l to a plurality of targets, each occurring within amutually exclusive one of successive ambiguous range intervals, for eachof the several pulse repetition frequencies employed; and

F 10. t; is a representative timing diagram, illustrating the sequenceof cooperation among the secondary storage channels and range intervalresolver logic means.

Referring to H6. ll, there is illustrated in block diagram form a pulsedenergy system embodying the inventive concept. There is provided a radartransmitter 10 having a gated system trigger input from a mutuallyexclusive one of at least two pulse repetition frequency sources ill, l2and 113. Each such source ofa mutually exclusive pulse repetitionfrequency may be comprised of countdown means 119 commonly responsive toa master clock 14 or the like. The system trigger input lfi oftransmitter MB is gatingly coupled to sources ll, 112 and 13 by means ofgates 16, I17 and 18 each of which gates has a gate control input tocount-down means 119.

In normal operation of the transmitter MD of FIG. l, the system triggerinput 115 of transmitter Ml is responsively coupled to the output ofeach of sources ll, l2 and 13 in sequence, each source being coupled fora preselected number (say, 250) of pulse repetition intervals, as shownby the representative time history of FIG. 2.

The echoes of the transmitted pulse received during the gating intervalassociated with each lPlRF, are clutter-referenced (by means wellunderstood) and then written into or stored by doppler storage means 20aor Zilb as a data matrix or doppler map of successive range tracesignals, and then cross-read at the output of such storage means, anddoppler-filtered by filter 22. Such filter may also include thresholdingto clip those signal levels lying within the filter bandwidth andrepresenting noise. in practice, two doppler storage means 20a and 2%would preferrably be employed: one to be written into with range tracedata received during the current period that a given PRF is utilized bytransmitter ill), the write-in sweep of such doppler storage means beingsynchronized with the transmitter pulse repetition interval; theread-out of such doppler map (in storage 12th:) is made during thesubsequent interval that the next PRF is utilized by transmitter Ml,While the range trace data received during such subsequent interval (ata different PRIF) is being written into the second doppler storage meansZllb, in synchronism with the new transmitter pulse repetition interval.Such doppler storage and doppler filtering, including the duplexeddoppler storage, is described in the above-noted U. S. application Ser.No. 391,073 filed Aug. 18, 1964, by Forest Dynan et al. (now US. Pat.No. 3,408,647).

The thresholded and clutter-free reconstructed range-trace output of thedoppler storage means for these successive pulse repetition intervalsassociated with a given PRF is then stored in a mutually exclusivestorage channel of multiple channel secondary storage means 23. When adoppler-filtered range trace signal for each successively-employed PRFis then stored in an associated storage channel of multiple channelsecondary storage means 213, the range trace data in each channel iscorrelated with that stored in the other channels by means of aplurality of range interval resolver logic elements 2 3.

The utilization of the secondary storage and logic means to resolveambiguous range indications may be more fully appreciated from aconsideration of the nature of such ambiguous intervals, as illustratedin FIGS. 3, ia, 4b, 4c, 5, (6a, 6b, 6c, 7 and FIG. 3 illustrates threeexemplary time histories of the response of a radar system, pulsed ateach of three different pulse repetition frequencies, in detection of atarget at a range-time T within the smallest (PRL) of the three pulserepetition intervals employed. Because the target range time is lessthan the smallest of the pulse repetition intervals employed, it isclear that such target return is also within the other pulse repetitionintervals utilized (l-Rl IPRI +A'l and IRl PRL TJ Thsretqrelhssraarsn trsstrstur linsli1; T and T observed for a respective one of the threepulse repetition intervals is equal to the true target return time Tinotherwords, the apparent range time interval observed is notunambiguous. Accordingly, the doppler read-out of the doppler mapconstructed for each of such three PlRlFs will provide a reconstructedrange trace signal demonstrating a target return at a common rangeinterval (T T, T T as shown in lFlGS. do, 4b and 4c.

lf, however, such target return (in response to a transmitted pulse)occurs in a pulse repetition interval subsequent to the pulse repetitioninterval associated with such particular transmitted pulse, then theindicated range time T is ambiguous, in that it is indicative of atarget range time T nPRl 'l",,, where n is an integer number. The secondpulse repetition interval following the transmitted pulse is thus afirst (n 1) ambiguous interval, while the (n 1) pulse repetitioninterval is the nth ambiguous interval. (The first pulse repetitioninterval following the transmitted pulse is of course the (n 0)ambiguous, or non-ambiguous, interval).

For example, where the target range time T is ob served as a targetreturn occurring in the second puise repetition interval following thetransmitted pulse, as shown in F165, then the indicated range times T Tand 13, for the several pulse repetition intervals (at which a dopplerbuild-up will be observed, as shown in lFlGv 2., 3a, 6b and 6c, inresponse to such target, will be different:

T lPRilg -l- T (Pill, +A'l') (T AT) 7 T llrtl i (FRl -l 2Aiy-tt, 21M)or, for the ambiguous interval, n l:

T TM Zll'l Where, for the least pulse repetition interval utilized, PRL,the apparent target range T is greater than the range time incrementdifference (HAT) between such pulse repetition interval and a successiveone, then the expressions for the apparent target range are related interms of the number n of ambiguous pulse repetition intervals and suchrange time increment:

or, for the ambiguous interval, n:

in M T T nAT T T, 2nd? Such relationship is more clearly indicated inthe composite diagram of Fit]. '7 in which the exemplary response tofive targets is displayed for each of three pulse repetition intervals(where PlRl, 238 ,usec, and AT 12 usec), each of the rive targetsreturns occurring in a mutually exclusive one of five successiveambiguous intervals n 0, l, 2, 3, and 4). it is to be appreciated, then,that if the read-outs from the several channels of the multiple channelstorage means 24 of FIG. l are appropriately time-phased in relation toeach other, so as to place in registry the correspondingdoppler-processed target signals from a single common tar get, then thetrue range time of such target may be determined from such time-phaserelation.

For example, if the read-out of the range trace signal from the secondchannel of secondary storage means 24 (of FlG. l) is delayed by AT,relative to that of channel l, then a target echo occurring in the firstambiguous interval (n l, in FlG. 7) of both channels 1 and 2 (i.e., forPRFs No. l and No. It) would occur si multaneously or in registry. inother words, a delay AT is added to the second channel apparent targetrange time T (in FIG. '7), whereby the second channel target signaloccurs simultaneously with the first channel target signal for targetsdetected in the first ambiguous range interval;

Al 'l' All ('l', -A'l") T, Accordingly the true target range time isdetermined as the sum of the apparent range time and such number (n l)of ambiguous range intervals:

T nPRl, T FRI, T it is to be further appreciated that the true rangetime T for any ambiguously indicated target may be generally determinedas (nlRl', T where n is the integer multiple of delay AT employed toeffect registry between corresponding target signals read-out ofchannels l and 2 of storage means 24 (in FIG. ll). Where multiplechannel secondary storage means 24 is comprised of magnetic storagemeans, such time delays (AT, 2AT...nAT) may be provided, for example, bysuitable spacing of each ofa plurality of read heads relative to areference read-out position of a storage drum, each spaced read-head forthe second storage channel corresponding to a mutually exclusive one ofsuch delays. Coincidence gating means or AND-type logic gates may beemployed to determine the coinci dence of the occurrence of a targetsignal readout on channel No. It of storage means 24 (in FIG. 1) and theoccurrence of a target signal read-out at one of the read heads ofsecond channel No. 2.

Where the apparent target range time "l, is small enough, and the truerange time (rzllRl T is great enough, the number n of ambiguousintervals involved in terms of Pl-Rl (for operation of the radar at PRFNo. i) may be different than the number associated with lRl (foroperation of the radar at PRF No. 2). Such result is referred to hereinas fold-back, and is indicated in H6. 7 for PRF No. 3 for the target atambiguous range interval n 3 (or T 3PRI T,,,), the target return for thePRF No. 3 transmitter pulse (for interval :1 3) occurring coincidentallywith the PRF No. 3 transmitter pulse. For the illustrated target rangetime 1",; 4PM, T occurring at ambiguous interval, 21 4 for PRF No. l,the corresponding PRl Nov 3 target range time T occurs in the thirdambiguous interval. in other words, for a given apparent range time Toccurring for PRF No. l in a successive one of n ambiguous rangeintervals. the corresponding response to PRF No. 2 or PRF No. 3 will bea successive shorter T or T within a like ambiguous range interval.until such apparent range interval for suchhigher PRF approaches zero.In the event of such latter limiting case. the target signal for an evenmore distant target will appear in that ambiguous interval for suchhigher lRF as that ambiguous interval preceding the one in which itappears at the lower or reference PRF. Thus, the like I; readhead forchannel 2 or 3 corresponding to that n-interval of PRl, for which anapparent target is detected. will not provide a second target signalread-out coincident with than in Channel l for resolving the rangeambiguity.

Accordingly, a third PRF (PRF No. 3) and associated doppler storage andsecondary storage therefor may be employed by range interval resolverlogic to overcome such folclbaclc. in other words, any two of the threechannels may be correlated. In addition to overcoming such foldbackeffect, the use of such additional PRF aids in reducing blind frequencyeffects occurring at either one of the other two PRFs, which mask thetarget and prevent target correlation for range ambiguity resolution.

Such ambiguity resolution data (nAT) and the apparent target range timedata, T may be employed by a targeting computer to indicate the truerange ofthe target (T nAT T,,).

The sequence of secondary storage write-in, read-out and the resolutionof range ambiguity by the arrangement of FlG. l for those exemplarypulse repetition frequencies indicated in FIG. 7 is depicted on H6. 8,indieating a representative processing interval of 1.035 seconds.

Thus, there has been described correlation means for time-domaincorrelation of a pair of doppler-processed range trace signals, eachrepresenting a different pulse repetition interval, the correlationbeing performed as a function of discrete range time nAT, where n is aninteger including zero and AT is the range time difference between therespective pulse repetition intervals. Therefore, an improved AMTI rangeambiguity resolver has been described.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample only and is not to be taken by way of limitation, the spirit andscope of this invention being limited only by the terms of the appendedclaims.

I claim: 1. In a pulsed energy system employing at least a pair of pulserepetition frequencies, means for resolving an ambiguous rangeindicative of a detected moving target and comprising doppler processingmeans responsive to target echo signals received by a receiver of saidsystem for providing at least a pair of clutter-free range tracesignals, each said range trace signal indicative of the system responseto a mutually exclusive one of said pulse repetition frequencies; andcorrelation means for time-domain correlation of said pair of rangetrace signals as a function of discrete time nAT, and comprising aplurality of coincidence detection means for comparing one of said rangetrace signals and a delayed second one of said range trace signals, asuccessive one of said plurality of coincident detection means employinga successively increased delay (nAT) of said delayed second range tracesignal, where n is an integer number including zero and where ATcorresponds to the range time difference between the respective pulserepetition intervals associated with said pair of pulse repetitionfrequencies. 2. The device of claim 1 in which said dopplerprocessingmeans includes a pairof time-duplexed doppler storage means, eacharranged to be responsive to the pulse repetition interval ofa selectedone of said system pulse repetition frequencies for providing a dopplermap; and

doppler filter means having an input arranged to be responsive to analternate one of said doppler storage means for providing a clutter-freerange trace output signal. 3. The device of claim 1 in which saidcorrelation means includes multiple channel secondary storage meansresponsively coupled to an output of said doppler processing means,.each channel of said storage means being responsive to the clutter-freerange trace signal associated with a mutually exclusive one of saidpulse repetition frequencies, for providing concomitant read-out of saidtwo range trace signals, one of said range-trace signals being read-outat successive delays nAT relative to the other of said range tracesignals, where n is an integer number including zero and AT correspondsto the range time difference between the pulse repetition intervalsassociated with said pair of pulse repetition frequencies;-and

coincidence gate logic means responsive to said readout of one of saidchannels and respective ones of said delayed readouts of the other ofsaid channels for indicating that integer number (n) of ambiguous pulserepetition intervals associated with the apparent range time for adetected moving target.

4. The device of claim 1 in which said correlation means includesmultiple channel secondary storage means responsively coupled to anoutput of said doppler processing means, each channel of said storagemeans being responsive to the clutter-free range trace signal associatedwith a mutually exclusive one of said pulse repetition frequencies, forproviding I concomitant read-out of said two range trace signals,range-time registration of one of said range-trace signals beingsuccessively delayed nAT relative to the other of said range tracesignals, where n is an integer number including zero and AT correspondsto the range time difference between the pulse repetition intervalsassociated with said pair of pulse repetition frequencies; and

ambiguity resolver logic means comprising a plurality (n l) ofcoincidence gates each responsive to said read-out of one of saidchannels and to a mutually exclusive of said delayed read-outs of theother of said channel for indicating that integer number (n) ofambiguous pulse repetition intervlas associated with the apparent rangetime for a detected moving target.

5. In a pulsed energy system employing at least a pair of pulserepetition frequencies and adapted for substantially clutterreferenceddetection of moving targets, means for resolving the ambiguous rangeindication of a detected moving target occurring at a range greater thanthat corresponding to the least pulse repetition interval provided bysaid pulse repetition frequencies, and

means responsive to a clutter referenced video receiver output of saidsystem for providing that doppler map associated with each of said pulserepetition frequencies, a preselected range time increment difference(AT) existing between the pulse repetition intervals of at least two ofsaid pulse repetition frequencies;

a thresholded doppler bandpass filter responsive to a doppler read-outof successive ones of said doppler maps for providing a substantiallyclutter-free range trace output;

multiple-channel recording means responsively coupled to an output ofsaid filter for separately recording the successive clutter-freerange-trace outputs, a first channel of said recording means having areference read head, and a successive channel of said recording meanshaving a preselected number of regularly spaced read heads, the spacingbetween adjacent readheads corresponding to a range time increment ofsaid recorded range trace outputs, the phase-spacing of a reference readhead on said successive one (n) of said channels differing from that ofsaid first channel by an amount corresponding to the preselected rangetime incremental difference (nAT) therebetween; and

a like plurality of logic means as said preselected number of read headsper successive channel, each logic means responsive to said read-head ofsaid first channel and to a mutually exclusive one of the read heads ofa successive channel of said recording means for providing a two-statelogic output indicative of the coincidence of any two of the inputsthereto from said multiple channel recording means for indicating thatinteger number (n) of ambiguous pulse repetition intervals associatedwith the apparent range time T,, ofa detected moving target.

6. In a pulsed energy system employing at least a pair of pulserepetition frequencies, the combination comprising means for operating atransmitter of said system at a successive one of a preselectedplurality of pulse repetition frequencies for a preselected number ofsuccessive pulse repetition intervals;

doppler processing means responsive to target echo signals received by areceiver of said system for providing at least a pair of clutter-freerange trace signals, each said range trace signal indicative of thesystem response to a mutually exclusive one of said pulse repetitionfrequencies; and

correlation means for time-domain correlation of said pair of rangetrace signals as a function of discrete time nAT, and comprising aplurality of coincidence detection means for comparing one of said rangetrace signals and a delayed second one of said range trace signals, asuccessive one of said plurality of coincident detection means employinga successively increased delay (nAT) of said delayed second range tracesignal, where n is an integer number including zero and where ATcorresponds to the time difference between the pulse repetitionintervals associated with said pair of pulse repetition frequencies,whereby the true range time of the target may be determined as the sumof the apparent range time and that delay (nAT) associated with theregistry coincidence of a portion of said one of said range tracesignals with a portion of said delayed other one of said range tracesignals.

1. In a pulsed energy system employing at least a pair of pulserepetition frequencies, means for resolving an ambiguous rangeindicative of a detected moving target and comprising doppler processingmeans responsive to target echo signals received by a receiver of saidsystem for providing at least a pair of clutter-free range tracesignals, each said range trace signal indicative of the system responseto a mutually exclusive one of said pulse repetition frequencies; andcorrelation means for time-domain correlation of said pair of rangetrace signals as a function of discrete time n Delta T, and comprising aplurality of coincidence detection means for comparing one of said rangetrace signals and a delayed second one of said range trace signals, asuccessive one of said plurality of coincident detection means employinga successively increased delay (n Delta T) of said delayed second rangetrace signal, where n is an integer number including zero and whereDelta T corresponds to the range time difference between the respectivepulse repetition intervals associated with said pair of pulse repetitionfrequencies.
 2. The device of claim 1 in which said doppler processingmeans includes a pair of time-duplexed doppler storage means, eacharranged to be responsive to the pulse repetition interval of a selectedone of said system pulse repetition frequencies for providing a dopplermap; and doppler filter means having an input arranged to be responsiveto an alternate one of said doppler storage means for providing aclutter-free range trace output signal.
 3. The device of claim 1 inwhich said correlation means includes multiple channel secondary storagemeans responsively coupled to an output of said doppler processingmeans, each channel of said storage means being responsive to theclutter-free range trace signal associated with a mutually exclusive oneof said pulse repetition frequencies, for providing concomitant read-outof said two range trace signals, one of said range-trace signals beingread-out at successive delays n Delta T relative to the other of saidrange trace signals, where n is an integer number including zero andDelta T corresponds to the range time difference between the pulserepetition intervals associated with said pair of pulse repetitionfrequencies; and coincidence gate logic means responsive to saidread-out of one of said channels and respective ones of said delayedreadouts of the other of said channels for indicating that integernumber (n) of ambiguous pulse repetition intervals associated with theapparent range time for a detected moving target.
 4. The device of claim1 in which said correlation means includes multiple channel secondarystorage means responsively coupled to an output of said dopplerprocessing means, each channel of said storage means being responsive tothe clutter-free range trace signal associated with a mutually exclusiveone of said pulse repetition frequencies, for providing concomitantread-out of said two range trace signals, range-time registration of oneof said range-trace signals being successively delayed n Delta Trelative to the other of said range trace signals, where n is an integernumber including zero and Delta T corresponds to the range timedifference between the pulse repetition intervals associated with saidpair of pulse repetition frequencies; and ambiguity resolver logic meanscomprising a plurality (n + 1) of coincidence gates each responsive tosaid read-out of one of said channels and to a mutually exclusive ofsaid delayed read-outs of the other of said channel for indicating thatinteger number (n) of ambiguous pulse repetition intervlas associatedwith the apparent range time for a detected moving target.
 5. In apulsed energy system employing at least a pair of pulse repetitionfrEquencies and adapted for substantially clutter-referenced detectionof moving targets, means for resolving the ambiguous range indication ofa detected moving target occurring at a range greater than thatcorresponding to the least pulse repetition interval provided by saidpulse repetition frequencies, and means responsive to a clutterreferenced video receiver output of said system for providing thatdoppler map associated with each of said pulse repetition frequencies, apreselected range time increment difference ( Delta T) existing betweenthe pulse repetition intervals of at least two of said pulse repetitionfrequencies; a thresholded doppler bandpass filter responsive to adoppler read-out of successive ones of said doppler maps for providing asubstantially clutter-free range trace output; multiple-channelrecording means responsively coupled to an output of said filter forseparately recording the successive clutter-free range-trace outputs, afirst channel of said recording means having a reference read head, anda successive channel of said recording means having a preselected numberof regularly spaced read heads, the spacing between adjacent readheadscorresponding to a range time increment of said recorded range traceoutputs, the phase-spacing of a reference read head on said successiveone (n) of said channels differing from that of said first channel by anamount corresponding to the preselected range time incrementaldifference (n Delta T) therebetween; and a like plurality of logic meansas said preselected number of read heads per successive channel, eachlogic means responsive to said read-head of said first channel and to amutually exclusive one of the read heads of a successive channel of saidrecording means for providing a two-state logic output indicative of thecoincidence of any two of the inputs thereto from said multiple channelrecording means for indicating that integer number (n) of ambiguouspulse repetition intervals associated with the apparent range time TA ofa detected moving target.
 6. In a pulsed energy system employing atleast a pair of pulse repetition frequencies, the combination comprisingmeans for operating a transmitter of said system at a successive one ofa preselected plurality of pulse repetition frequencies for apreselected number of successive pulse repetition intervals; dopplerprocessing means responsive to target echo signals received by areceiver of said system for providing at least a pair of clutter-freerange trace signals, each said range trace signal indicative of thesystem response to a mutually exclusive one of said pulse repetitionfrequencies; and correlation means for time-domain correlation of saidpair of range trace signals as a function of discrete time n Delta T,and comprising a plurality of coincidence detection means for comparingone of said range trace signals and a delayed second one of said rangetrace signals, a successive one of said plurality of coincidentdetection means employing a successively increased delay (n Delta T) ofsaid delayed second range trace signal, where n is an integer numberincluding zero and where Delta T corresponds to the time differencebetween the pulse repetition intervals associated with said pair ofpulse repetition frequencies, whereby the true range time of the targetmay be determined as the sum of the apparent range time and that delay(n Delta T) associated with the registry coincidence of a portion ofsaid one of said range trace signals with a portion of said delayedother one of said range trace signals.